A study of the role of mica in the bloating of clays has been made. Eighteen samples of clay supplied by the Geological Branch of the South Australian Mines Department, were used for the tests, which consisted of heating the samples in an electric furnace to bloating temperature, with and without mica additions, and determining the bulk specific gravity of the fired specimens. The mica used in the tests was a flotation concentrate prepared from Radium Hill mill tailings and contained a mixture of the common mica minerals. The results of the tests indicate that mica has little or no effect on the bloating characteristics of the clay types examined. Several clays on heating appeared to reach plasticity and if gas had been evolved bloating would have been possible. Bloating was also evident at the contact between some samples and the mild steel tray on which heating took place. Further work is recommended.